1. Field of the Invention
This invention relates to an image forming apparatus, such as an electrophotographic copier, a printer or the like, and a process kit which is detachable relative to the image forming apparatus, and to an image forming apparatus which includes a blade-like cleaning member for cleaning an image carrying member after the transfer of an image and a blade-like charging member provided at a downstream side in the direction of movement of the image carrying member from the blade-like cleaning member, and a process kit which is detachable relative to the image forming apparatus.
2. Description of the Related Art
As concrete examples of the image forming apparatus of the type as described above, there exists an electrophotographic copier using a transfer method, an electrostatic recording apparatus using a transfer method, and the like.
In an electrophotographic copier using a transfer method, a drum-type or endless-belt-type electrophotographic photosensitive member which rotates or which is rotatably driven is used as an image carrying member, and a developed image is formed by applying an image forming process means based on uniformly charging the surface of the photosensitive member, and exposing and developing an image on the surface. The developed image is then transferred to the surface of a transfer material by a transfer means, the transferred developed image is fixed on the surface of the transfer material by a fixing means, and the transfer material is output as the copied image. The surface of the photosensitive member after the transfer of the image is cleaned by a cleaning means, and is repeatedly utilized for forming images.
In an electrostatic recording apparatus using a transfer method, a drum-type or endless-belt-type dielectric member which rotates or which is rotatably driven is used as an image carrying member, and a developed image is formed by applying an image forming process means based on uniformly charging the surface of the dielectric member, selectively removing electric charges from the surface and developing an image formed on the surface. Subsequently, the transfer and fixing operations of the developed image to the surface of a transfer material is executed in the same way as in the above-described electrophotographic copier, and the transfer material is output as the recorded image. The surface of the dielectric member after the transfer of the image is cleaned by a cleaning means, and is repeatedly utilized for forming images.
The cleaning means removes untransferred developer (toner), paper powder of the transfer material and other adhering contaminants which remain on the surface of the image carrying member (photosensitive member, dielectric member or the like) after the transfer of the image to the transfer material. A rubber elastic member made of urethane rubber or the like is generally used as the cleaning member, which is configured so that contaminants adhered on the surface of the image carrying member are wiped off and removed by contacting the cleaning member with the surface of the image carrying member.
As the means for uniformly charging the surface of the image carrying member, a corona discharge unit having a corona wire electrode and a shield electrode surrounding it and having a uniform charging property, such as a corotron, a scorotron or the like, has widely been used. However, the corona discharge unit has problems in that an expensive high-voltage power supply is needed. Further, miniaturization is difficult since certain minimum spacing is needed, such as a shield space for applying high voltage to the wire electrode, and the like. Furthermore, since corona byproducts, such as ozone and the like, are generated in a large amount, additional means and mechanisms are needed for dealing with the by-products, all of which are factors which tend to make the apparatus large and costly.
Accordingly, adoption of a contact charging method in place of a corona charging unit has recently been investigated. In the contact charging method, electric charges are directly injected onto the surface of an image carrying member by contacting a conductive member (a contact charging member), to which voltage (for example, D.C. voltage of about 1-2 kV (kilovolts), superposed voltage of D.C. voltage and A.C. voltage, or the like) is applied from a power supply, to the surface of the image carrying member as a member to be charged. The surface of the image carrying member is thereby charged at predetermined potential. There have been devised a roller charging method (Japanese Patent Public Disclosure (Kokai) No. 56-91253 (1981)), a blade charging method (Japanese Patent Public Disclosure (Kokai) Nos. 56-104349 (1981) and 60-147756 (1985)), a charging and cleaning method (Japanese Patent Public Disclosure (Kokai) No. 56-165166 (1981)), and the like.
In the contact charging method, it is important for the charging member to contact each portion of the image carrying member uniformly along its longer direction. If a uniform contact state is not provided, there is produced an unevenly charged state on the surface of the image carrying member.
From the viewpoint of providing a simplified and low-cost apparatus, the blade charging method as disclosed, for example, in the aforementioned Japanese Patent Public Disclosure (Kokai) No. 56-104349 (1981) is most preferred.
In some cases, however, uniform charging is not obtained due to abrasion and damage of the surface of the image carrying member caused by the fact that a blade-like contact charging member and a blade-like cleaning member contact the image carrying member in a fixed state nearly standing still relative to the movement of the image carrying member.